Today, a considerable amount of attention is riveted to electrically powered vehicles, such as an electric car and a hybrid car, as environment-friendly vehicles. These vehicles are equipped with an electric motor for generating a traveling drive force and a rechargeable power storage device for storing electric power to be supplied to the electric motor. Examples of the hybrid car are a vehicle equipped with an internal combustion engine as a power source in addition to the electric motor, and a vehicle equipped with a fuel battery as a direct current power source for driving the vehicle in addition to the power storage device.
In some known hybrid cars, an in-vehicle power storage device can be charged by an electric power source outside of the vehicle as with electric cars. An example of such hybrid cars is, what is called, a “plug-in hybrid car”, in which a household electric power source can be used to charge the power storage device such that a vehicle charging port is connected to a plug socket provided in a house by a charging cable.
Meanwhile, a power transmission method attracting attention in recent years is wireless power transmission in which neither a power supply code nor a power transmission cable is used. Three known technical methods are prevalently employed in the wireless power transmission; power transmission by using electromagnetic induction, power transmission by using electromagnetic wave, and power transmission by using a resonance technique.
Of these techniques, the resonance technique is a non-contact power transmission technology wherein a pair of resonators (for example, a pair of self resonant coils) is resonated in an electromagnetic field (near field) so that electric power is transferred by way of the electromagnetic field. This technique enables the transmission of such a large electric power as a few kW over a relatively long distance (for example, a few meters) (see the Patent Document 1 and Non-Patent Document 1).    Patent Document 1: WO 2007/008646    Non-Patent Document 1: Andre Kurs et al., “Wireless Power Transfer via Strongly Coupled Magnetic Resonances”, [online], Jul. 6, 2007, SCIENCE, Volume 317, pp. 83-86, [Searched on Sep. 12, 2007], Internet <URL; http://www.sciencemag.org/cgi/reprint/317/5834/83.pdf>